Industrial process for preparing planar blanks for the manufacture of hollow turbineblades



United States Patent INDUSTRIAL PROCESS FOR PREPARING PLANAR BLANKS FOR THE MANUFACTURE OF HOL- LOW TURBINE BLADES Jean-Baptiste Paul Van, Sannois, France, assignor to Societe Nationale dEtude et de Construction dc Moteurs dAviafion, Paris, France, a French company No Drawing. Filed July 19, 1957, Ser. No. 672,870

Claims priority, application France July 31, 1956 5 Claims. (Cl. 2-9-531) It has already been contemplated to manufacture gas turbine blades and, in particular, hollow blades, from planar blanks, through various shaping operations, (folding, forging, etc.) which put the material to comparatively hard conditions which are liable to adversely afiect the mechanical characteristics of the material. One of the most detrimental troubles is due to the internal strains of divergent directions in the sheets plane and more generally to the lack of homogeneity of the mechanical characteristics of the used material. Thus, in particular, the elastic limit is not the same at every point of the metal sheet. The rolled sheets in the compositions of steel used for blades are generally delivered with a range of elastic limits as wide sometimes as 50%. On the other hand, the subsequent shaping operations cause local colddrawing resulting in an increased elastic limit in only certain parts of the materials.

The object of the present invention is to improve the strength of the pieces, by raising the elastic limit of the metal in the whole piece up to a precise and uniform value, determined by taking into consideration both the manufacturing requirements and the crack resistance of the finished pieces.

Accordingly, the invention relates to a process for improving the resisting properties of a sheet of a metal, the stress-strain diagram of which exhibits a smooth and gradual curvature in the region of yield, and making them quite identical at any point of the sheet and from one sheet to another one, said process comprising the steps of tensioning a planar sheet of metal of the aforesaid character while keeping it quite plane throughout, of giving to the tensioning force per unit of surface of the sheet cross-section a value situated in the region of yield of said stress-strain diagram of the metal considered, and making uniform both the breadth and thickness of the sheet by removing material therefrom, whereby the metal of the sheet is given an increased elastic limit and the local new elastic limits at the various points of the sheet are approached closer to equality.

The local new elastic limits are equal to what may be called the final specific stresses, i.e., the quotient of the total tensioning force by the local cross-sections of the sheet at the end of the tensioning step, the sheet crosssections decreasing progressively and differently from a cross-section to another during the tensioning step, since the local initial elastic limits are not the same at the various points of the sheet.

This tensioning method, which is often applied in conventional laboratory tests of materials, as well as to the shaping or planishing of sheets, is industrially used, according to the present invention, for obtaining, as regards the blank sheets, by tensile cold-drawing, predetermined elastic limit characteristics, providing thus a new industrial product having an accuracy which cannot be obtained by ice rolling, especially in the case of high strength and high cold-drawing coefiicient alloys, such as refractory stainless steels used in gas turbines. j

The tensioning can be performed either in one operation or in several stages, each successive tensioning op eration being then carried out after a preceding operation for making uniform the cross-section of the sheet by removing material in breadth and thickness, throughout the sheet.

During the tensioning the total tensile stress is -adjusted and maintained to the value corresponding to the product of the real cross-section of the sheet, at the selected level, by the specific strain corresponding to the desired elastic limit.

The tensioning operation can be carried out by means of any adequate machine, for instance, on a laboratory pulling machine (of the Amsler machine type) which has suflicient power and is equipped with convenient jaws.

The tensioning operations by stages depend upon the desired precision. Through these stages one can progressively rectify the local cross-section variations that may occur on account of the constitution or structural heterogeneity or of mechanical characteristics the effect of which is very perceptible, more particularly for heavy cold-drawings of compound metals. Through said stages one may also and principally rectify the ends of the sheet where the cross-sections do not undergo the same variations than the remainder of the sheet on account of the proximity of the jaws; if this rectifying were not made before the next pulling, said effect of the jaws would force to take away the parts near to the jaws and would result finally in material losses that are not trifling. Mainly, for this last reason the last tensioning step should, advantageously, cause only a small cold-drawing just to get a final equalization of the local elastic limits.

The industrial product obtained according to the invention consists in a sheet of a precise thickness, slightly or moderately cold-drawn, having a uniform and accurately determined elastic limit as well as high-standard planar qualities. This product is particularly suitable for mass production of pieces requiring a very high precision, in particular of hollow turbine blades by cold mechanical shaping.

The product may also be made of a similar sheet, but more cold-drawn, until near the breaking point if it is desired. Such a product is suitable for pieces that have to undergo important strains without permanent deformations.

What is claimed is:

1. A process for obtaining uniform properties on a large area of a ductile metal sheet, the elastic limit of which can be increased by cold-drawing producing a permanent deformation, comprising at least one cycle of two successive operations, namely, the steps of tensioning said sheet while maintaining it very flat during the drawing operation, giving the tensile stress a value in the region of yield of the stress-strain diagram of the metal in order to produce a slight permanent deformation, and making the sheet strictly uniform in breadth and thickness by removing material therefrom.

2. A process in accordance with claim 1 wherein the drawing is carried to the extent of establishing said elastic limit of the metal sheet at a point close to the breaking point of the metal from which the sheet is made.

3. A process in accordance with claim 1 wherein said operation of prodiicing uniform thickness is done while the sheet is under tension 'but always after a certain relaxation of the maximum tension that has just been used.

4. A process in accordance with claim 11 wherein said uniformity of thickness operation is done on the sheet after releasing all traction efior-t on said sheet.

5. Process according to claim 1, characterized by the fact that the final traction effort exerted on the sheet is regulated in such a. manner as to produce the desired elastic limit for the section of the sheet remaining after the thickness and the point-bypoint elastic limit of thesheet have been made strictly uniform.

References Cited in the file of this patent UNITED STATESBATENTS 1,190,986 Hudson Feb. 20, 1940 4 2,263,423 McKee Nov. 18, 1941 2,723,445 Trautvetter Nov. 15, 1955 2,805,470 Frokjaer-Jensen Sept. 10, 1957 2,852,062 Lorant Sept. 16, 1958 5 2,867,260 Ungerer Ian. 6, 1959 OTHER REFERENCES Boyd, James E.: Strength of Materials, McGraw-Hill 10 Book Company Inc., New York, 1924, pp. 4445.

The Making, Shaping. and Treating of Steel; 5th ed., 1940; p. 1160.

Metals Handbook, 1948 edition, page 5, produced by 15 American Society for Metals. 

1. A PROCESS FOR OBTAINING UNIFORM PROPERTIES ON A LARGE AREA OF A DUCTILE METAL SHEET, THE ELASTIC LIMIT OF WHICH CAN BE INCREASED BY COLD-DRAWING PRODUCING A PERMANENT DEFORMATION, COMPRISING AT LEAST ONE CYCLE OF TWO SUCCESSIVE OPERATIONS, NAMELY, THE STEPS OF TENSIONING SAID SHEET WHILE MAINTAINING IT VERY FLAT DURING THE DRAWING OPERATION, GIVING THE TENSILE STRESS A VALUE IN THE REGION OF YIELD OF THE STRESS-STRAIN DIAGRAM OF THE METAL IN ORDER TO PRODUCE A SLIGHT PERMANENT DEFORMATION, AND MAKING THE SHEET STRICTLY UNIFORM IN BREADTH AND THICKNESS BY REMOVING MATERIAL THEREFROM. 